Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $243.95   8.828%   $265.4859   $265.49   $265.50   $265.50  
  Purchase #2 $20.61   10.369%   $22.7471   $22.75   $22.75   $22.70  
  Purchase #3 $134.33   6.156%   $142.5994   $142.60   $142.60   $142.60  
  Purchase #4 $91.81   9.304%   $100.352   $100.35   $100.35   $100.40  
  Purchase #5 $250.82   9.239%   $273.9933   $273.99   $274.00   $274.00  
  Purchase #6 $70.48   4.501%   $73.6523   $73.65   $73.65   $73.70  
  Purchase #7 $137.85   11.377%   $153.5332   $153.53   $153.55   $153.50  
  7 purchase totals = $949.85       $1,032.3632   $1,032.36   $1,032.40   $1,032.40